Gas turbine stator

ABSTRACT

The invention concerns a gas turbine stator comprising:  
     at least first injection means ( 1 ) providing a passage for a main cooling air stream into a pressurised chamber ( 16 );  
     means for evacuating discharge air coming from an internal labyrinth gland ( 13 ) of a first cavity ( 9 ) towards a lower-pressure second cavity ( 10 );  
     second injection means for evacuating the air contained in said second cavity ( 10 ) towards a main duct.  
     The inventive stator is characterised in that it further comprises third injection means designed to generate an overpressure close to the internal labyrinth gland ( 13   a  and  13   b ) in said pressurised chamber ( 16 ).

TECHNICAL FIELD

[0001] The technical field of this invention is that of gas turbines,such as axial-flow turbine engines, comprising a stator notably intendedto supply air to other elements of the gas turbine. This stator inparticular, is a mechanical unit, which allows relatively cool air to besupplied to the blades of the high-pressure turbine, this air intendednotably to cool a part of the rotor being drawn from the bottom of thecombustion chamber.

STATE OF THE PRIOR ART

[0002] In well-known embodiments of gas turbine stators of the priorart, we usually find an element such as a main injector which makes itpossible to accelerate the air drawn from a cavity in the stator, aretainer for guiding the air down to the blades of the high-pressureturbine, as well as different air circuits making it possible tocalibrate all the airflows throughout the system. These airflows arethen injected into different cavities consequently making it possible tolimit the rise in temperature of the mechanical components. According tothese different types of embodiments, widespread use is made ofleakproof systems such as labyrinth glands to limit as much as possiblethe leakage of cool air.

[0003]FIG. 1 represents a longitudinal half section of a statoraccording to the prior art. The purpose of this stator is to draw coolair from the stator cavity 20, then deliver this air through slopinghole type injectors 21 which speed it up and adjust the direction offlow thereof. This cool air then arrives in a pressurised chamber 22before entering into orifices 23 of the retainer so as to be directedtowards the blades 24 of the rotor 34. This main cooling air stream issymbolised by the arrow A in FIG. 1. The arrow B symbolises the flow ofdischarge air coming from the internal labyrinth gland 35, intended tobe re-injected into the main duct. Still referring to FIG. 1, we seethat in order to allow this flow of discharge air we commonly use pipes25 welded to different parts of the stator.

[0004] However, even though the labyrinth glands are commonly used torender the pressurised chamber leakproof, as notably disclosed in thedocument FR 2744761, these labyrinth glands cannot stop all the airleaks through this chamber. In particular, the internal labyrinth glandcannot stop some of the hot air present outside the pressurised chamberfrom penetrating into the latter. This consequently generates anincrease in temperature of the pressurised chamber, and thus a reductionin the efficiency of the cooling system of the rotor.

OBJECT OF THE INVENTION

[0005] The aim of the invention is therefore to present a gas turbinestator resolving all the aforementioned inconveniences, thusimplementing a device limiting as much as possible the leakage of hotair towards the inside of the pressurised chamber.

[0006] To accomplish this, the object of the invention is a gas turbinestator comprising:

[0007] a first injection means providing a passage for a main coolingair stream into a pressurised chamber;

[0008] a means for evacuating discharge air coming from an internallabyrinth gland of a first cavity towards a lower-pressure secondcavity;

[0009] a second injection means for evacuating the air contained in saidsecond cavity towards a main duct.

[0010] According to the invention, the stator is made in such a way thatit further comprises a third injection means for generating anoverpressure of air close to the internal labyrinth gland in saidpressurised chamber.

[0011] The main advantage of this invention is the maximum limitation ofhot air discharges, at the internal labyrinth gland heading towards thepressurised chamber. The limiting of these discharges slows down theincrease in temperature in the inside of the pressurised chamber, thusmaking it possible to draw less cool air via the first injection means.

[0012] Preferably, the stator according to the invention is made so thatthe first injection means comprise at least one blade for producing aflow of air tangent to the rotor.

[0013] This configuration presents the advantage of bringing the airinto excellent conditions, thus greatly reducing the rise in temperaturedue to the passage of air in the ducts. These rises in temperature arealso limited due to the nature of the first injection means in the shapeof blades with an appropriate aerodynamic profile, these means thushaving identical behaviour to that of a conventional axial manifold.

[0014] The evacuation means used in this invention preferably compriseat least one piercing emerging on one hand into the first cavity and onthe other hand into the second cavity.

[0015] According to this particular embodiment implementing piercings toallow for the evacuation of discharge air, an advantage of the inventionresides in the reduction in manufacturing costs by using an existingpart instead of adding pipes as per the prior art. This stator accordingto the invention also participates in the lightening of the injectors,as well as the lengthening of the service life of the stator due to theabsence of welding of the pipes as is of common practice.

[0016] Preferably, the piercings implemented to accomplish the means ofevacuating discharge air are carried out in the solid part of the bladesconstituting the first injection means.

[0017] According to a particular embodiment of the invention, thesupport of a part of the internal labyrinth gland comprises the firstinjection means. This support has a honeycomb structure alternativelymade of cavities and blocks of material. The cavities are thus intendedto lead to the evacuation means whereas the blocks of material comprisethe third injection means.

[0018] Advantageously, the stator according to the invention can thenhave a crossover system for three flows of air assembled in a singlepart capable of being made in a single casting. We note that thisparticular configuration of the invention makes it simple to assemblethe different elements of the stator.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] This description will be based on the annexed drawings amongwhich:

[0020]FIG. 1, previously described, illustrates the prior art;

[0021]FIG. 2 represents a longitudinal half section of one part of aturbine engine in which is fitted the stator according to the invention;

[0022]FIG. 3 represents a perspective partial view of the statoraccording to the invention emphasising the co-operation between thefirst injection means and the means for evacuating discharge air;

[0023]FIG. 4 represents a longitudinal half section of one part of aturbine engine in which is fitted the stator according to the invention,when this turbine engine uses a harpoon type retainer.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0024] In reference to FIG. 2, we see one part of a turbine enginenotably comprising a stator according to the invention. This statorfirstly comprises a pressurised chamber 16 delimited by differentelements. Among these elements there is an external labyrinth gland 4 aand 4 b as well as an internal labyrinth gland 13 a and 13 b. These twointernal and external labyrinth glands 13 a, 13 b, 4 a and 4 b arerespectively held by a support 14 fixed to the wall of a stator cavity 5and another support 36 fixed to this support 14. The internal labyrinthgland 13 a and 13 b partly delimits a boundary between the pressurisedchamber 16 and a first cavity 9 adjacent to it, whereas the externallabyrinth gland 4 a and 4 b partly delimits a boundary between thepressurised chamber 16 and a second cavity 10 also adjacent to it. Thefirst and second cavities 9 and 10 are themselves separated by thesupport 14. It is to be noted that the stator has, downstream from thesecond cavity 10 in the direction of the flow of a main duct of the gasturbine represented by the arrow C in FIG. 2, a third cavity 37separated from the second cavity 10 by the support 36.

[0025] The internal 13 a, 13 b, and external 4 a and 4 b labyrinthglands are generally broken down into at least one friction part 13 aand 4 a fixed to the stator via supports 14 and 36 and at least one lip13 b and 4 b fixed to a retainer 2. This retainer 2 also delimits thepressurised chamber 16 and is fixed to a rotor 38 of the gas turbine.This retainer 2 comprises injection holes 6 emerging into a cavity 7located between said retainer 2 and the rotor 38 of the gas turbine, thelatter having blades 8.

[0026] The stator firstly comprises first injection means 1 achieved inthe support 14 and making it possible to draw cool air from the statorcavity 5, so as to send it towards the blades 8 of the rotor 38. As inthe devices of the prior art, this air passes through the firstinjection means 1 to enter the pressurised chamber 16, where a maincooling air stream transits before cooling the blades 8 of the rotor 38passing through the injection holes 6 designed for this purpose in theretainer 2.

[0027] Once through the injection holes 6 the cold air fills the cavity7 located between the retainer 2 and the rotor 38. This retainer 2 is toensure the sending of this air down to the blades 8 of the rotor 38.

[0028] Still with reference to FIG. 2, the stator comprises means forevacuating discharge air coming from the internal labyrinth gland 13 aand 13 b so as to evacuate the air out of the first cavity 9 adjacent tothe pressurised chamber 16, towards the second cavity 10 of lowerpressure. These means of evacuating air can be fixed to the support 14.

[0029] Additionally, the stator comprises second injection means forevacuating air held in the second cavity 10 in order to re-inject itinto the third cavity 37 so that it may rejoin the main duct of the gasturbine. These second injection means are located in the part of thesupport 36 that separates the second and third cavities 10 and 37.

[0030] According to the invention, the stator also comprises thirdinjection means to generate an overpressure of air in the pressurisedchamber 16, the local overpressure being located close to the internallabyrinth gland 13 a and 13 b. The purpose of these means is to hinderas much as possible the hot air of the first cavity 9 from escapingtowards the pressurised cavity 16, so that the latter remains at anacceptable temperature. The purpose of these third injection means is togenerate a local overpressure in the pressurised chamber 16 close to theinternal labyrinth gland 13 a and 13 b in order to balance the pressuresbetween this pressurised chamber 16 and said first cavity 9 itself beingadjacent. The cool air drawn by these third injection means comes fromthe same stator cavity 5 as the air drawn by the first injection means 1to generate the main cooling air stream.

[0031] The stator is equipped with first injection means 1 whose shapeand manufacture greatly differ from prior embodiments. Indeed, inreference to FIG. 3, these injection means comprise at least one blade12 making it possible to render the flow of air coming from the statorcavity 5 tangent to the rotor 38. These first injection means 1 are thuscomparable to a conventional axial manifold, thus bringing the air underbetter conditions than if it had to pass through sloping piercings, aswas commonly used in the past. The direct consequence of using such adevice is the elimination of a bursting effect due to the jet on theretainer 2, a major source of temperature rise of the supply air to theblades. This bursting effect is the consequence of using slopingpiercings to introduce the air into the pressurised chamber. Indeed, theslope of these piercings is insufficient to prevent the main air streamfrom being directly projected against the retainer 2. The collisionbetween this flow of cool air and the retainer 2 results in the cool airin the pressurised chamber 16 unnecessarily heating up thus renderingthe ventilation less efficient. It is to be specified that the inventioncould, however, use conventional first injection means, such as thesloping injection holes as previously disclosed.

[0032] According to a particular embodiment of the invention, the meansfor evacuating discharge air preferably comprise at least one piercing11 in the support 14, these piercings 11 emerging on one hand into thefirst cavity 9 and on the other hand into the second cavity 10. Thisfurther makes it possible to reduce the manufacturing costs by using anexisting part to achieve these evacuation means, contrary to thesolutions involving adding pipes and then welding them to differentelements of the stator. Additionally, the incorporating of such atechnical solution makes it possible to increase the service life of thestator due to the absence of the welding of the pipes. In theaforementioned embodiment of the first injection means 1, we can notablycarry out these piercings 11 in a part of the blades 12. As can be seenin FIG. 3, the blades 12 are solid and can consequently contain thesemeans for evacuating discharge air. The making of simple piercings inthe material of these blades 12 thus makes it possible to compact theunit constituted by the first injection means 1 as well as the means forevacuating discharge.

[0033] With reference to FIG. 2, we see that all of these previouslydescribed three flows, namely the one coming from the first injectionmeans 1, the one coming from the third injection means as well as theone coming from the means for evacuating discharge air, can exist withinthe same part.

[0034] To achieve this, it is then possible to adapt the support 14 sothat it can receive these three flows. This support 14 is partlyhoneycombed, notably thanks to the presence of cavities 20 capable ofdirecting the flow of air towards the evacuation means. The piercings 11for the passage of air start in the cavities 20 and cross the blades 12as previously described. Additionally, to achieve the honeycombedstructure, these cavities 20 are set between blocks of material 15 inwhich the third injection means are made.

[0035] Furthermore, as the support 14 comprises the first injectionmeans 1, we obtain a triple-flow stator, these flows crossing in thesupport 14 without any of them disturbing the smooth flowing of theothers. This part of the stator can easily be made in a single casting.Additionally, the use of casting technology makes it possible to adjustthe shapes and mould as best as possible the rotor 28, giving it a morecompact appearance than before. This reduction in the overall size ofthe parts of the rotor 38 also leads to substantial reductions inmanufacturing costs due to the restricted dimensions of these partsconstituting the rotor 38.

[0036] The third injection means can be in the form of at least onepiercing 3 through the blocks of material 15. These piercings arepreferably sloping to obtain a flow of air with a large componenttangent to the rotor 38, namely according to a perpendicular directionto the sectional plane in FIG. 2. It is also possible that these thirdinjection means take the form of at least one blade to render the flowof air tangent to this rotor 38. These blades would then be of the sametype as those of the first injection means represented in FIG. 3.

[0037] To evacuate the air in the second cavity 10 towards the mainduct, there are the second injection means. As this is the case inreality, we can carry out at least one sloping piercing 17 in the statorso as to obtain a flow of air with a large component tangent to therotor. These piercings 17 can be made in the support 36 between thesecond cavity 10 and the third cavity 37. Note that we can also resortto a blade system with the previously described thermal and mechanicaleffects. Additionally, the air coming from these second injection meanscan also be used to cool a zone of the rotor subject to high flowtemperatures from the main duct.

[0038] Likewise, the second injection means can also improve theefficiency of the rotating leakproof systems of the retainer 2. Inreference to FIG. 4, the piercings 17 emerge into a cavity 18 of theexternal labyrinth gland. This case arises when a harpoon type retainer2 is used, namely when the external labyrinth gland is made so that eachlip 26, 27 and 28 works in conjunction with a distinct honeycomb typefriction part 29, 30 and 31. Due to this particular layout we thusobtain at least two cavities 18 and 19 partially separated from thesecond cavity 10 by an element other than one of the honeycomb typefriction parts 29, 30 and 31.

[0039] We can then inject air into one of these cavities 18 or 19 viathe second injection means. This air swirls when arriving in thecavities 18 and 19 and is driven in rotation before being naturallysucked from the pressurised chamber 16 towards the main duct, due to thepressure difference between these elements. The injecting of hot airinto one of these cavities 18 or 19 will thus allow a reduction in thecold air to be drawn from the first injection means 1 and consequentlyresults in an improvement in the performance of the system. Also notethat injecting air into the small cavity 18 created by the succession oftwo labyrinths increases the pressure of this small cavity and thusprovokes an additional drop in the pressure difference between thiscavity 18 and the pressurised chamber 16.

[0040] The main added benefit here lies in the use of a harpoon typeexternal labyrinth gland. Indeed, this layout makes it possible to makethe second injection means in a solid element, other than a honeycombtype friction element, which would disturb the air jet. The solutionproves to be very advantageous in that it avoids the disturbances due topassing through honeycomb structures 29, 30 and 31, and in that it hasfewer manufacturing constraints than the current solutions of the priorart.

[0041] The second injection means thus take the form of slopingpiercings 17 to obtain a flow of air with a large component tangent tothe rotor 38, or the form of blades such as those that can be used tomake the first injection means 1. The overpressure generated in thesmall cavity 18 considerably reduces the discharge rates of the coolingcircuit, with the consequence that more cold air coming from the firstinjection means manages to pass through the passage holes 6.

[0042] Another particularity of the invention lies in the specificlayout of the support 14 and of the first injection means 1.Traditionally, the part of the support 14 holding the friction part 13 aof the internal labyrinth gland 13 a and 13 b is placed under the airoutlet of the first injection means 1. In this configuration, this partof the support 14 is then subject to minor displacements engendered bythese first injection means 1, thus creating major discharges throughthe internal labyrinth gland 13 a and 13 b. To compensate for thisinconvenience, the stator can then have, as can be seen in FIG. 2, a gapbetween the outlet of the first injection means 1 and the part of thesupport 14 holding the friction part 13 a. This gap makes it possible tointerpose between these two elements the third injection means, whichalso engender minor displacements of the support 14 holding the frictionpart 13 a. It is thus possible to control the clearance in the internallabyrinth gland 13 a and 13 b, by decoupling the aforementioned twomovements of the stator. Indeed, by adjusting the mass of the blocks 15,the air flow rates in the piercings 3 and the number of these piercings,it is thus possible to adjust the relative position of the rotor and thestator in order to limit as much as possible any eventual dischargesthrough this internal labyrinth gland 13 a and 13 b.

[0043] The same is true of the external labyrinth gland 4 a and 4 b.Indeed it is possible to control the minor displacements of the support36 holding the friction 14 part 4 a, by combining the effects of theinertia mass of this support 36 and the effects of the cooling generatedby the sloping piercings 17 of the second injection means.

[0044] The third injection means also make it possible to obtain atop-up flow rate for the cooling air circuit of the blades, as well asstabilisation of the pressure in the pressurised chamber 16.

[0045] Finally, note that the support 36 of the friction part 4 a isbolted from the inside, contrary to common practice, this techniquemaking it possible to save space in the external part for the supportingof the manifold.

[0046] Naturally, various modifications can be made by a person skilledin the art to the device that has been described, solely as anon-restrictive example.

1-12. (Canceled). 13 A gas turbine stator comprising: first injectionmeans for providing a passage for a main cooling air stream into apressurized chamber; means for evacuating discharge air coming from aninternal labyrinth gland partly delimiting the pressurized chamber of afirst cavity towards a lower-pressure second cavity; second injectionmeans for evacuating the air contained in said second cavity towards amain duct; and third injection means for generating an overpressure ofair close to the internal labyrinth gland in said pressurized chamber.14 A gas turbine stator set forth in claim 13, wherein the firstinjection means comprises at least one blade for generating a flow ofair tangent to a rotor of the gas turbine. 15 A gas turbine stator setforth in claim 13, wherein the first injection means comprises at leastone sloping hole for generating a flow of air with a large componenttangent to a rotor of the gas turbine. 16 A gas turbine stator set forthin claim 13, wherein the means for evacuating comprises at least onepiercing emerging into the first cavity and into the second cavity. 17 Agas turbine stator set forth in claim 14, wherein the means forevacuating comprises at least one piercing emerging into the firstcavity and into the second cavity. 18 A gas turbine stator set forth inclaim 17, wherein each piercing is made in a solid part of one of theblades. 19 A gas turbine stator set forth in claim 17, wherein theinternal labyrinth gland comprises at least one friction part, eachfriction part being held by a support in which is located the firstinjection means, the support being honeycombed by cavities and blocks ofmaterial, the cavities configured to lead to the means for evacuatingdischarge air and the blocks of material configured to comprise thefirst, second, and third injection means. 20 A gas turbine stator setforth in claim 19, wherein the third injection means comprises at leastone blade for generating a flow of air tangent to a rotor of the gasturbine. 21 A gas turbine stator set forth in claim 19, wherein thethird injection means comprises at least one piercing made through theblocks of material. 22 A gas turbine stator set forth in claim 21,wherein at least one piercing is made sloping to produce a flow of airwith a large component tangent to a rotor of the gas turbine. 23 A gasturbine stator set forth in claim 13, wherein said second injectionmeans comprises at least one sloping piercing for producing a flow ofair with a large component tangent to a rotor of the gas turbine. 24 Agas turbine stator set forth in claim 13, wherein said second injectionmeans comprises at least one blade for producing a flow of air tangentto a rotor of the gas turbine. 25 A gas turbine stator set forth inclaim 13, wherein the pressurized chamber is delimited by a harpoonexternal labyrinth gland, creating at least two cavities, each of thetwo cavities being partly separated from the second cavity by a solidelement, said second injection means emerging into at least one of thetwo cavities being made in the solid element.